Add complevel argument to netcdf exporter + tests

[ladc]

As pointed out by @larsbonnefoy, setting this to a lower value significantly speeds up netcdf writing.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.17%. Comparing base (a1dd4a7) to head (af0873d).

Additional details and impacted files

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##           master     #550   +/-   ##
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  Coverage   84.17%   84.17%           
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  Files         170      170           
  Lines       14985    14985           
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  Hits        12614    12614           
  Misses       2371     2371           

Flag	Coverage Δ
unit_tests	84.17% <ø> (ø)

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[larsbonnefoy]

To complement @ladc pr, when using compression Level 9 the bottleneck when exporting is the compression leading to slow netcdf writes. Lowering the compression level only slightly increases output size but improves overall execution speed. This would help overall speed up without having to rely on other parallelization methods.

Another change we could implement is to be able to rely on other compression libraries than zlib.

[larsbonnefoy]

Adding simple new argument to exporter + test, looks got for me

[Copilot]

Pull request overview

Adds a complevel argument to initialize_forecast_exporter_netcdf so users can trade off netCDF compression ratio for write speed (the previous behavior hard-coded complevel=9). The default is preserved at 9 for backward compatibility, and the test matrix is extended with several compression-level values.

Changes:

• Add complevel parameter (default 9) to initialize_forecast_exporter_netcdf and forward it to both createVariable calls.
• Document the new parameter in the docstring.
• Extend test_io_export_netcdf_one_member_one_time_step parametrization with a complevel dimension.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
pysteps/io/exporters.py	Replaces hard-coded complevel=9 with a user-configurable argument.
pysteps/tests/test_exporters.py	Adds complevel to the parametrized test cases (but does not pass it through to the exporter).

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.